Carbohydrate Hydrogen-Bonding Cooperativity − Intramolecular Hydrogen Bonds and Their Cooperative Effect on Intermolecular Processes − Binding to a Hydrogen-Bond Acceptor Molecule

Abstract

The high hydroxy (OH) group content in carbohydrates makes the study of carbohydrate OH···XH and OH···X H-bond energetics fundamental to understanding of carbohydrate recognition. There is, however, a relative lack of knowledge concerning the factors that allow a carbohydrate to participate in recognition events stabilised by intermolecular H bonds. We therefore present here a systematic study on the factors that determine the formation of a well-defined intramolecular H-bonding network between carbohydrate hydroxy groups, and its cooperative or anti-cooperative influence on selected intermolecular processes mediated by H bonds. With this in mind, we first determined the H-bonding networks of a series of carbohydrate derivatives − monoalcohols, 1,2- and 1,3-diols and amidoalcohols − by 1H NMR and FT-IR spectroscopy. The hydroxy groups of these compounds showed different abilities to form intramolecular H bonds, depending on their relative positions and configurations on the pyranose ring, and on the nature of the adjacent functional groups. It has also been shown that both the directionality and strength of the intramolecular H-bonding network of a carbohydrate govern the formation of cooperative or anti-cooperative H-bond centres, with consequent repercussions on the thermodynamics of the intermolecular H-bonding interactions of the carbohydrate in question. From this study, some general rules for the prediction of the intramolecular H-bonding network characteristics of a given carbohydrate and its influence on the energetics of intended intermolecular recognition processes have been inferred. The results presented here give a new perspective over understanding of the role of the H-bonding interactions in carbohydrate recognition and have fundamental implications for the rational design of glycoconjugates incorporating H-bonding motifs with geometrical and electronic complementarity to given receptor molecules.